The full skin friction and full end-bearing resistances of a single pile are not mobilized at the same displacement, while the conventional approach often oversimplifies by adding the skin friction to the end-bearing resistance as independent calculation steps. This paper presents a simplified interaction approach for the nonlinear load–settlement analysis of a single pile considering simultaneously the degradation of skin friction resistance and end-bearing resistance hardening under varying loads. The ability to estimate the load–settlement response of piles based on either needed loads or settlement is a special benefit of the proposed approach over existing methods. In addition, the proposed model is able to separate the skin friction resistance, end-bearing resistance, and elastic compression at arbitrary settlement. The analytical method shown a satisfactory performance as compared to experimental results for three extensively studied field test situations. The suggested approach shows promise as a suitable solution for the design optimization as well as the preliminary analysis to organize a suitable loading test program. A parametric analysis is conducted to further examine the influence of various significant parameters related to the load–settlement response of piles.

The study and application of soil arching theory in geosynthetic-reinforced pile-supported (GRPS) embankments have gained increasing attention, as accurate arching estimation significantly influences load-deflection behavior of structures. While most existing models rely on Rankine's earth pressure theory, which applies primarily to granular soils and neglects cohesion effects. This paper employs three-dimensional numerical simulations to examine the impact of soil cohesion on soil arching mechanisms in pile-supported embankments. Results indicate that cohesion enhances load transfer to piles, with arching efficacy increasing nonlinearly before stabilizing at higher cohesion values. Building on these findings, the ground reaction curve (GRC) model is proposed to predict arching behavior in both cohesive and non-cohesive embankments at various deformation stages. By integrating critical state soil mechanics with the concentric arch model, the transition between maximum and critical arching states is captured through changes in the mobilized friction angle with relative displacement. Model validation against two well-instrumented case studies demonstrates its accuracy, particularly in accounting for soil cohesion. Moreover, the maximum arching model better predicts GRPS embankments under small deformations (relative displacement <4 %), while the critical arching model is more suitable for large deformations (relative displacement >6 %). The proposed model effectively captures arching behavior improvements in both cohesive and non-cohesive soils.

One of the most crucial tasks in the design, control, and construction of urban deep excavations is ensuring the safety of the existing underground infrastructure. Deformation and settlement created by excavation may damage the adjacent tunnels. In this study, the stability of an existing triple tunnel in relation to the construction of an adjacent deep excavation is evaluated by numerical simulation using both the discrete-element method (DEM) and the finite-element method (FEM). A deep excavation supported by the retaining wall and five levels of strutting system was created adjacent to an existing triple tunnel. The excavation’s width and depth were 30 and 16 m, respectively. In both discrete-element (DE) and finite-element (FE) simulations, the horizontal spacing of the triple tunnel wall relative to the retaining wall (SH) is varied between 3 and 35 m, while vertical spacing of the triple tunnel’s crown from the ground surface (SV) is changed from 4.8 to 32 m. The results indicated that at a certain value of SV and with increasing the SH, the horizontal displacement of the wall decreases. The variations in the triple tunnel position significantly affected the settlement pattern. In addition, the results showed that the maximum vertical displacement occurred at the middle tunnel crown, while the lowest value of the maximum vertical displacement was found at the crown of the right tunnel. At a certain value of the vertical displacement, the wall horizontal displacement is deduced by increasing in the SH value.

Due to the relatively different mechanical and physical properties of soils and structures, the interface plays a critical role in the transfer of stress and strain between them. The stability and safety of geotechnical structures are thus greatly influenced by the behavior at the soil–structure interface. It is therefore important to focus on the unique characteristics that set the interface apart from other geomaterials while examining the interface behaviour. Understanding the physical mechanism and modelling principles of these interfaces becomes a crucial step for the secure design and investigation of soil-structure interaction (SSI) issues. Moreover, to deal with this soil-environment interaction problem, the classical soil mechanics formulation must be progressively generalised in order to incorporate the effects of new phenomena and new variables on SSI behaviour. Considering the variety of energy geostructures that are emerging nowadays, it is crucial to comprehend the thermo-hydro-mechanical (THM) behaviour of the interface. The objective of this study is to fill this information gap as concisely as possible. A critical review is provided along with the state-of-the-art information on the thermo-hydro-mechanical behaviour of the soil-structure interface, including testing tools and measurement methods, basic principles and deformation mechanisms, constitutive models, as well as their applications in numerical simulations. This study explains how loading influences the mechanisms at the interface and critically examines the effects of boundary conditions, soil properties, environmental factors, and structure type on the THM behaviour of interface zones between soils and structural elements. The validity and reliability of the interface shear stress-displacement models are also covered in this paper. Lastly, the trends and recent advancements are also recommended for the interface research.

This work presents a simplified method for the nonlinear analysis of the load–displacement response of piles in multi-layered soils. As a starting step, a new interface model based on the disturbed state concept (DSC) is put forth to simulate the interface shear stress-displacement relationship by considering the nonlinear hardening–softening behaviour. In the new model, input parameters can be conveniently calibrated using conventional interface shear tests or on-site tests. The good agreement between predictions and experimental data from interface direct shear tests validated the performance of the proposed DSC model. The DSC model performed better in terms of predictions when compared to the hyperbolic one. Next, the soil-structure interface model and bearing capacity theory are coupled to provide a theoretical framework for the analysis of pile load-transfer in saturated and unsaturated multi-layered soils, where the DSC model is employed to represent base resistance as well as skin friction. This work also discusses the profile of steady-state in-situ matric suction, soil–water characteristic curve, and pore-water pressure of unsaturated soils. The proposed method has the advantage of being used in practice as it is simple to obtain input parameters from laboratory tests, as well as Standard Penetration or Cone Penetration Tests. The proposed framework is finally applied to the analysis of five well-documented case studies. The proposed approach and the static load test results from the field measurements are found to be in satisfactory agreement, indicating that the proposed method performs well. The proposed method is suggested to be utilised for preliminary analysis, planning a suitable programme of loading tests, as well as optimizing the pile design by back analysis of the load test results.

The bearing resistance of energy piles in the presence of temperature effects has not been thoroughly investigated, preventing the perfecting of energy pile design methods. Quantifying the relationship between soil suction and the temperature of unsaturated soils therefore becomes an important step in predicting the bearing resistance of energy piles. A new constitutive model based on interfacial energy and thermodynamic theories is therefore presented to predict the effect of temperature on soil suction as well as the soil–water characteristic curve (SWCC) in this paper. The analytical model for the nonisothermal matric suction was developed by combining five different temperature-dependent functions for the surface tension, air–water contact angle, void ratio, and thermal expansion of solid and water density, thereby providing a more complete approach than the one that considers surface tension only. The proposed formulation was expressed under a simplified form which is believed to be a useful and convenient tool to apply to a range of possible field situations. The temperature-dependent relationship of soil suction was then used to extend existing isothermal SWCCs to nonisothermal conditions that allow obtaining the SWCC at any temperature. The validity of the proposed model was verified by comparison to several test data sets for five different soils: swelling clay, hard clay, clayey–silty soil, ceramic material, and sand. The satisfactory agreement between predicted and measured curves proved that the proposed model had good performance in predicting the effect of temperature on the SWCCs of unsaturated soils. The nonisothermal SWCC model was then coupled with bearing resistance theory to produce a simplified method for analysis of energy piles. The results showed that the proposed method successfully predicted pile resistance at various temperatures when compared to experimental data. The pile resistance reduced as the temperature rose for a specific degree of saturation or if the soil was in an undrained condition. However, water evaporation may cause a decrease in water content and an increase in matric suction as the temperature increases. Therefore, as soils dry out, pile resistance may increase with increasing temperature.

The prediction of shear strength of unsaturated soils remains a significant challenge due to their complex multi-phase nature. In this paper, a review of prior experimental studies is first presented in order to outline important pieces of evidence, limitations and some design considerations. Then, an overview of existing shear strength equations is summarised, with a brief discussion. A micromechanical model with stress equilibrium conditions and multi-phase interaction considerations is presented to provide a new equation for predicting the shear strength of unsaturated soils. The validity of the proposed model is examined using published shear strength data for different soil types. The shear strength predicted by the analytical model was found to be in good agreement with the experimental data and to provide high performance in comparison with existing models. Evaluation of the results using two criteria – the average relative error and the normalised sum of squared error – proved the effectiveness and validity of the proposed equation. Using the proposed model, a non-linear relationship between shear strength, saturation degree, volumetric water content and matric suction was observed.

The effect of soil density on the soil–water characteristic curve (SWCC) is becoming a topic of universal interest due to the heterogeneity of soils and environmental variables. In this study, a simple and effective model based on the idea of translating the particle-size distribution curve to the SWCC is proposed for predicting SWCC change with initial density. There is only one new parameter introduced, and it is easily calibrated using two SWCCs obtained from test data. The SWCCs for the same soil at different initial void ratios can be estimated using the developed model. Several existing models are also thoroughly examined, with an emphasis on the advantages and disadvantages of each model. The validity of the proposed model was then verified by comparing it to three other models and experimental data for eight different types of soils. The proposed model also outperforms other existing models in this extensive study, providing good and consistent prediction performance across various soils. The proposed model is then applied to different engineering challenges involving the estimation of bearing resistance of unsaturated soils. Three typical examples chosen for illustration in this paper are the effect of soil density variation on unsaturated shear strength, bearing capacity of a shallow foundation, and ultimate bearing resistance of an energy pile. The findings of the investigation reveal that the proposed model can be utilized to solve a variety of problems involving soil–structure interaction in unsaturated soils.

In unsaturated soil mechanics, the soil–water retention curve (SWRC) continues to play an important role, since it provides the necessary links between the properties and behaviour of unsaturated soils with a variety of engineering challenges. The temperature has been identified as the main factor influencing SWRC as compared to a variety of other parameters. The goal of this research is to describe theoretical and experimental aspects of the temperature effect on unsaturated soil water retention phenomena. Theoretically, a brief review of the constitutive laws governing the thermal-hydro-mechanical (THM) behaviour of unsaturated soils is presented, along with links between variations in suction with water content, temperature, and void ratio. It also provides a broad framework that would to be well adapted to describing many specific circumstances. Through a closed-form predictive relationship that is developed in this framework, the effect of temperature is examined. By using this relationship, the soil–water retention curve at arbitrary temperature could be determined from one at a reference temperature, therefore significantly decreasing the number of tests necessary to describe the thermo-hydro-mechanical behaviour of a soil. Besides, the SWRC of kaolinite clay was also measured at three different temperatures in an experimental program. The test findings reveal that when the temperature rises, the SWRC decreases significantly. The experimental results were then integrated with sixteen other available data sets covering a wide range of soil types, densities, and suction to create a complete verification program for analytical models. The proposed model has a good performance and reliability in forecasting the fluctuation of non-isothermal SWRC than any existing model, according to statistical assessment results. The analytical model can be used to examine the thermo-hydro-mechanical characteristics of unsaturated soils in numerical simulations.

The soil–water characteristic curve (SWCC) plays an important role in solving the stability and deformation problems of unsaturated soils. In many practical situations, soils are usually experienced by both deformations and thermal conditions. In this interest, the paper proposes a simple and effective model to predict the combined effect of initial density and temperature on the SWCC and to be able to quantify the changes in thermal-hydro-mechanical behavior of unsaturated soils. In the first step, an initial density-dependent SWCC model is presented using the translation principle between particle-size distribution curve and soil–water characteristic curve. In the second part, a non-isothermal model is proposed to predict the effect of temperature on the SWCC. The key to the non-isothermal model is considering five different temperature-dependent functions, which are surface tension, contact angle, particle-size expansion, void ratio, and water density. On the basis of 22 data sets of thermal volume change, this study also developed further a theoretical correlation between void ratio and temperature that is directly related to soil plasticity. It was observed that the value of the thermal void ratio increases as soil plasticity increases, and there is a nonlinear relationship between the plasticity index and the void ratio. Because of this, soils with high plasticity are more susceptible to volume changes caused by temperature fluctuations than soils with low plasticity. A coupled mechanical–thermal model is then produced which is capable to predict separately or simultaneously the effect of temperature and initial density on SWCC. The proposed model is validated against several test data sets available in the literature. The results show that the proposed model has a good performance in predicting the variation in SWCC with arbitrary temperature and initial density.